This invention is related generally to the delivery of chemicals to a wellbore during petroleum production operations. In one embodiment, the invention relates to a method for delivering chemicals through a subsurface safety valve while maintaining suitable protection of the well in the event that the control of fluid flow from the well is lost.
During typical hydrocarbon production operations in a producing well, it may be desirable to add chemicals from a surface facility into the producing well to facilitate the production of liquids from the well or to protect the well from erosion, corrosion or scale build-up. Foaming agents may be added to the well to mitigate the effect of an accumulation of liquids in the production tubing. Under certain conditions, the accumulated liquids (e.g. liquid water or condensate) may restrict the upward flow of fluids through the tubing to the surface facility. Using the foaming agent to converting at least a portion the liquid in the production tubing to a foam helps reduce the back pressure created by the condensate and permits higher hydrocarbon recovery rates from the well. Chemicals, such as foam-forming chemicals, may be added into the production tubing through small diameter tubing which passes down into the well within the production tubing. Scale inhibitors and corrosion inhibitors may be added in the same way to help protect the integrity of the production tubing against chemical attack or degradation.
One feature of many modern wells is a subsurface safety valve (SSV) which is fitted into production tubing in the wellbore, generally several hundred feet below mudline. Subsurface Safety Valves operate to block the flow of formation fluids upwardly through the production tubing should a failure or hazardous condition occur at the surface facility or within the production tubing itself. The SSV typically employs a valve closure member, or “flapper,” that is moveable between an open position and a closed position, with the flapper pivotally mounted to a hard seat. In its open position, the flapper pivots away from the hard seat, thereby opening the bore of the production tubing. However, the flapper is strongly biased to its closed position. When the flapper is closed, it mates with the hard seat and prevents hydrocarbons from traveling up the wellbore to the surface. The flapper plate of the safety valve is held open during normal production operations by the application of hydraulic fluid pressure transmitted to an actuating mechanism. A common actuating mechanism is a cylindrical flow tube, which is maintained in a position adjacent the flapper by hydraulic pressure supplied through a supply conduit extending to the surface facility. The supply conduit is normally installed within the annulus between the production tubing and the well casing. Hydraulic fluid within the supply conduit feeds against a piston. The piston, in turn, acts against the cylindrical flow tube, which in turn moves across the flapper within the valve to hold the flapper open. When a catastrophic event occurs at the surface, somewhere along the production tubing or within the hydraulic system, hydraulic pressure from the supply conduit is interrupted, causing the cylindrical flow tube to retract, and allowing the flapper of the safety valve to quickly close. When the safety valve closes, it blocks the flow of production fluids up the tubing. Thus, the SSV provides automatic shutoff of production flow in response to well safety conditions that can be sensed and/or indicated at the surface. Examples of such conditions include a fire on an offshore platform, sabotage to the well at the earth surface, a high/low flow line pressure condition, a high/low flow line temperature condition, and simple operator override. This feature is particularly important for underwater wells, where an uncontrolled fluid flow from the well would be very difficult to manage.
Producing wells with an installed chemical delivery system providing an uninterrupted length of tubing extending from the surface facility to the producing fluids within the well are incompatible with a fitted SSV, since the chemical delivery line extending through the SSV would interrupt the safe operation of the SSV. As a consequence, it is desirable to modify the chemical delivery system to achieve the desired compatibility with an SSV fitted into the production tubing. WO2007/073401 provides a first injection conduit in fluid communication with a first hydraulic port above a subsurface safety valve, a second injection conduit in fluid communication with a second hydraulic port below the subsurface safety valve, and a fluid pathway to bypass the valve and allow hydraulic communication between the first hydraulic port and the second hydraulic port.
U.S. Pat. No. 7,198,099 suggests supplying a chemical treatment fluid in a system which permits the use of the treatment fluid for controlling the subsurface safety valve within a wellbore. Treatment fluid is supplied at a pressure greater than a threshold pressure to maintain the valve in an open position, to permit hydrocarbon flow up through the production tubing. If the pressure within the treatment fluid supply line is increased beyond a second threshold pressure, a one-way check valve within the supply system opens, allowing treatment fluid to flow into a treatment fluid injection conduit and then into the well.